1. Field of the Invention
The present invention relates generally to a data processing system for reducing the data processing requirements for a phased array radar antenna, and more particularly pertains to a data processing system for reducing the data processing requirements for signals received by an electronically scanned radar antenna system formed by a linear array of endfire elements.
2. Discussion of the Prior Art
Ganz, et al. U.S. Pat. No. 4,336,543 discloses an electronically scanned antenna system having a linear array of endfire elements of the type for which the data processing system of the present invention was developed. In this antenna system, the endfire elements are laterally spaced between about 0.3.lambda. to 0.9.lambda. apart, preferably about 0.55.lambda. apart, to enhance the effects of mutual coupling therebetween for broadening the radiation signal pattern of the elements in the plane of the array. Advantageously, the endfire elements may be of the Yagi type with each endfire element including a common reflector, a driver, and a plurality of directors. This provides an antenna array of very small elevation so as to be suitable for conformal installation on or within the airfoil surfaces of an aircraft, e.g., wing leading edges and the horizontal stabilizer trailing edge. Such a phased array antenna system offer tremendous surveillance and missile guidance capability with.. high levels of jam resistance at reduced weight, power and volume.
One of the major developmental and production problems associated with such conformal linear phased array radars is accomplishing the level of interference suppression processing required for the many transmit/receive modules in the system array. Some current development work has focused on the UHF band at approximately 450 MHz. However, for some applications, operation at the L band, at approximately 900 to 1,200 MHz, is more desirable, but at the higher frequencies the relative signal processing requirement or load increases by a factor of two to three, or more, tending to mitigate against operation at the L band.
In conventional signal processing techniques for the signals received by each element of such a phased array antenna, the antenna is first operated to transmit, and by varying the transmitted gain and phase of each element module, the transmitted beam can be formed and steered in azimuth. Similarly, the receiver gain is varied, and the received signals phase shifted to match the transmitted beam pattern. In conventional signal processing techniques, the outputs of all of the element receivers are initially processed independently. In effect, the signal processing in the prior art was considered to be a function of the transmitted frequency, which determines the number of transmit/receive element modules required.
A conventional data processing technique would initially process separately the signal received from each of the twelve receive elements. Interference suppression is obtained by generating nulls in the receive antenna pattern in the direction of the interference. The nulls are produced by adjusting the phase and amplitude (weight) of the received signal from each array element just enough to null the interference with minimal impact on the rest of the antenna pattern. The extent that this can be accomplished depends upon the number of weights that are available for adjustment, usually referred to as the number of degrees of freedom.
If the phased array had twelve element modules therein, then twelve separate signal processing channels were required, each having a phase shifting circuit and a weighted amplifier controlled by an interference suppressor processor, and the twelve controlled signals were then summed to form a composite output signal. This technical approach resulted in a significant and burdensome signal processing requirement for the received signals.